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Description  |
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FIELD OF THE INVENTION
The present invention relates to a direct positive silver halide
photosensitive material and a process for forming an image by exposing the
photosensitive material and subjecting it to a surface developing process
to form a direct positive image.
BACKGROUND OF THE INVENTION
A photographic process for forming a direct positive image without
necessitating any reversal processing step or negative film is well known.
Known processes for forming a positive image by using a direct positive
silver halide photosensitive material except for special ones can be
mainly classified into two types from the viewpoint of practical
utilization as will be described below.
In one type of the processes, a previously fogged silver halide emulsion is
developed to produce a direct positive image by breaking the fog nuclei
(latent image) in the exposed region using solarization or according to
Harschel effects.
In the other type of the processes, an un-fogged silver halide emulsion of
internal latent image-type is imagewisely exposed, and the surface
development is conducted after the fogging process or during the fogging
process, to obtain a direct positive image.
The term "silver halide photographic emulsion of internal latent
iamge-type" indicates a silver halide photographic emulsion having a
photosensitive nucleus mainly inside the silver halide grains so that the
latent image is formed mainly inside the grains by the exposure.
As compared with the former processes, the latter processes have generally
a higher sensitivity and, therefore, they are suitably used when a high
sensitivity is required. The process of the present invention belongs to
the latter.
Various techniques have been known in this technical field. Typical
examples of them are described in U.S. Pat. Nos. 2,592,250, 2,466,957,
2,497,875, 2,588,982, 3,317,322, 3,761,266, 3,761,276 and 3,796,577 and
British Pat. Nos. 1,151,363, 1,150,553 and 1,011,062.
According to these known processes, photosensitive materials having a
relatively high sensitivity as compared with other ones of the direct
positive type can be prepared.
The details of the mechanism of the formation of the direct positive image
are described in, for example, T. H. James, "The Theory of The
Photographic Process", 4th Edition, Chapter 7, pages 182 to 193 and U.S.
Pat. No. 3,761,276.
Namely, it is generally considered that fog nuclei are formed selectively
on only the surface of the silver halide grains in an unexposed region by
the surface desensitization effect due to so-called internal latent image
formed inside the silver halide grains by the first imagewise exposure and
then an ordinary surface development process is conducted to form the
photographic image (direct positive image) in the unexposed region.
As processes for selectively forming the fog nuclei, there have been known
a "photo-fogging" process wherein the second exposure is conducted over
the whole surface of the photosensitive layer (see, for example, British
Pat. No. 1,151,363) and a "chemical fogging process" wherein a nucleating
agent is used. The latter process is described in, for example, Research
Disclosure, Vol. 151, No. 15162 (published in Nov., 1976), pages 76 to 78.
A direct positive color image is formed by imagewise exposure of a direct
positive silver halide photosensitive material followed by (1) a color
development conducted in the presence of a nucleating agent and/or fog
light and then (2) desilverization process.
It is known that the desilverization can be accelerated by using a
bleach-fixing solution containing both ferric complex salt of
aminopolycarboxylic acid and thiosulfate as described in German Pat. No.
866,605. However, when the ferric complex salt of aminopolycarboxylic acid
having an essentially weak oxidizing power (bleaching power) is combined
with the thiosulfate having a reducing power, the bleaching power of the
former is seriously deteriorated. Various processes have been proposed for
overcoming the defect of the bleach-fixing solution. They include, for
example, a process wherein an iodide or bromide is added as described in
British Pat. No. 926,569 and Japanese patent publication No. 53-11,854,
and a process wherein triethanolamine is used so that the reaction system
contains a high concentration of the ferric complex salt of
aminopolycarboxylic acid as described in Japanese Patent Public Disclosure
No. 48-95,834. However, the effects of these processes are yet
insufficient and unpractical.
The bleach-fixing solution has, as well as the defect of the insufficient
desilverization power, another defect that a cyan dye formed in the color
development is reduced into a leuco dye and the color development is
reduced into a leuco dye and the color reproducibility is seriously
deteriorated. Although it has been known that this defect can be overcome
by elevating the pH of the bleach-fixing solution as described in U.S.
Pat. No. 3,773,510, this process is impractical because the bleaching
power is weakened as the pH is elevated. In addition, the nucleating agent
is unstable under such a high pH condition and it is liable to be oxidized
by air. A process wherein the leuco dye is oxidized with a potassium
ferricyanide bleaching solution to recover the cyan dye again after the
bleach-fixing is described in U.S. Pat. No. 3,189,452. However, potassium
ferricyanide is causative of an environmental pollution as described above
and even when the bleaching is conducted after the bleach-fixing, the
effect of reducing the amount of remaining silver is scarcely exhibited.
On the other hand, as a process for increasing the bleaching power of the
ferric complex salt of aminopolycarboxylate when a photosensitive material
comprising a negative emulsion is bleached, a process has been proposed
wherein a bleaching accelerator selected from various ones is added to a
bleaching bath, bleach-fixing bath or preprocessing bath.
The bleaching accelerators include, for example, mercapto compounds
described in U.S. Pat. No. 3,893,858, British Pat. No. 138,842 and Japanes
Patent Public Disclosure No. 53-141623; compounds having a disulfido bond
as described in Japanese Patent Public Disclosure No. 53-95630;
thiazolidine derivatives as described in Japanese Patent Publication No.
53-9854; isothiourea derivatives as described in Japanese Patent Public
Disclosure No. 53-94927, thiourea deriviatives as described in Japanese
Patent Public Disclosure Nos. 45-8506 and 49-26586; thioamido compounds as
described in Japanese Patent Public Disclosure No. 49-42349; and
dithiocarbamates as described in Japanese Patent Public Disclosure No.
55-26506.
Although some of the bleaching accelerators have the effect of accelerating
the bleaching of the color photosensitive materials comrpising a negative
emulsion, the effect of them on the color photosensitive materials
comprising a positive emulsion is not always satisfactory and they do not
satisfy the requirement of reducing the processing time.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a process for forming a
direct positive color image, wherein the bleaching time can be reduced and
the color reproduction is not deteriorated. The above object can be
achieved by a process for forming a direct positive color image comprising
exposing a photosensitive material comprising, on a support, at least one
photographic emulsion layer containing previously unfogged internal latent
image-type silver halide grains and a color image-forming coupler,
color-developing the same in the presence of a nucleating agent/or fogging
light, and then processing it with a processing solution having a
bleaching effect, characterized in that a bleaching accelerator is
incorporated in a processing bath having the bleaching effect or a
pre-processing bath or the bleaching accelerator is incorporated in the
photosensitive material.
DETAILED DESCRIPTION OF THE INVENTION
Now, the present invention will be explained in detail below.
The bleaching accelerator to be contained in the bleaching bath in the
present invention is selected from compounds having a mercapto group or
disulfido bond, thiazoline derivatives, thiourea derivatives, and
isothiourea derivatives. Any compounds can be used so long as they have
bleaching-accelerating effects. Among them, those of the following general
formulae (I) to (VII) are preferred:
General formula (I):
##STR1##
wherein R.sub.1 and R.sub.2 may be the same or different and each
represent a hydrogen atom or a substituted or unsubstituted lower alkyl
group (preferably having 1 to 5 carbon atoms; particularly methyl, ethyl
or propyl group) or an acyl group (preferably having 1 to 3 carbon atoms;
such as acetyl or propionyl group), and n represents an integer of 1 to 3,
or R.sub.1 and R.sub.2 may be combined to form a ring.
R.sub.1 and R.sub.2 are particularly preferably a substituted or
unsubstituted lower alkyl group.
The substituents of R.sub.1 and R.sub.2 include, for example, a hydroxyl
group, carboxyl group, sulfo group, and amino group.
General formula (II):
##STR2##
wherein R.sub.3 and R.sub.4 have the same meaning as that of R.sub.1 and
R.sub.2 in the general formula (I) and n is an integer of 1 to 3, or
R.sub.3 and R.sub.4 may be combined to form a ring.
R.sub.3 and R.sub.4 are particularly preferably a substituted or
unsubstituted lower alkyl group.
The substituents of R.sub.3 and R.sub.4 include, for example, hydroxyl
group, carboxyl group, sulfo group, and amino group.
General formula (III):
##STR3##
General formula (IV):
##STR4##
General formula (V):
##STR5##
wherein R.sub.5 represents a hydrogen atom, halogen atom (such as chlorine
or bromine atom), amino group, substituted or unsubstituted lower alkyl
group (having preferably 1 to 5 carbon atoms; particularly preferably
methyl, ethyl or propyl group) or amino group having an alkyl group (such
as methylamino, ethylamino, dimethylamino or diethylamino group).
The substituents of R.sub.5 include, for example, a hydroxyl group,
carboxyl group, sulfo group and amino group.
General formula (VI):
##STR6##
wherein R.sub.6 and R.sub.7 may be the same or different and each
represent a hydrogen atom, substituted or unsubstituted alkyl group
(preferably a lower alkyl group such as methyl, ethyl or propyl group),
substituted or unsubstituted phenyl group or substituted or unsubstituted
hetercyclic group (in particular, a heterocyclic group having at least one
hetero atom such as nitrogen, oxygen or sulfur atom; for example, a
pyridine ring, thiophene ring, thiazolidine ring, benzooxazole ring,
benzotriazole ring, thiazole ring, or imidazole ring), R.sub.8 represents
a hydrogen atom or a substituted or unsubstituted lower alkyl group
(preferably having 1 to 3 carbon atoms; such as methyl or ethyl group).
The substituents of R.sub.6 to R.sub.8 include, for example, a hydroxyl
group, carboxyl group, sulfo group, amino group and lower alkyl groups.
R.sub.9 represents a hydrogen atom or carboxyl group.
General formula (VII):
##STR7##
wherein R.sub.10, R.sub.11 and R.sub.12 may be the same or different and
each represents a hydrogen atom or lower alkyl group (preferably having 1
to 3 carbon atoms; such as methyl or ethyl group) or R.sub.10 and R.sub.11
or R.sub.12 may be combined to form a ring, and X represents an amino
group, sulfonic acid group or carboxyl group which may have a substituent
(such as a lower alkyl group, e.g. methyl group, or an alkoxyalkyl group,
e.g. acetoxymethyl group).
Particularly preferably, R.sub.10 to R.sub.12 are a hydrogen atom, methyl
group or ethyl group, and X is an amino group or dialkylamino group.
Examples of the compounds of the general formulae (I) to (VII) are as
follows:
##STR8##
The above-described compounds can be prepared by a known process. In
particular, the processes for the production of the compounds are
described in U.S. Pat. No. 4,285,984, G. Schwarzenbach et al., Helv. Chim.
Acta., 38, 1147 (1955) and R. O. Clinton et al., J. Am. Chem. Soc., 70,
950 (1948) (for those of the general formula (I)), Japanese Patent Public
Disclosure No. 53-95630 (for those of the general formula (II)), Japanese
Patent Public Disclosure No. 54-52534 (for those of the general formulae
(III) and (IV)), Japanese Patent Public Disclosure Nos. 51-68568, 51-70763
and 53-50169 (for those of the general formula (V)), Japanese Patent
Publication No. 53-9854 and Japanese Patent Public Disclosure No.
59-214855 (for those of the general formula (VI)), and Japanese Patent
Public Disclosure No. 53-94927 (for those of the general formula (VII)).
The amount of the compound having a mercapto group or disulfido bond in the
molecule, a thiazoline derivative, or an isothiourea derivative, which are
to be incorporated in the bleaching solution usable in the present
invention, varies depending on the kind of the photographic material to be
processed, processing temperature, and processing time. It is usually
1.times.10.sup.-5 to 10.sup.-1 mol, preferably 1.times.10.sup.-4 to
5.times.10.sup.-2 mol per liter of the processing solution.
The compound of the present invention is usually added to the processing
solution after dissolution thereof in water, an alkaline, an organic acid
or an organic solvent. The compound in the form of a power can be directly
added to the bleaching bath and, in such a case, no influence is exerted
on the bleach accelerating effect.
The previously unfogged internal latent image-type (herein referred to as
"internal latent image-type") silver halide emulsion, usable in the
present invention is an emulsion of silver halide grains the surface of
which has not previously been fogged and in which the latent image is
formed mainly inside the grains. Preferably, when a given amount of the
silver halide emulsion is applied to a transparent support and exposed to
light for a given time in the range of 0.01 to 10 sec. and the development
is conducted in the following developer A (internal developer) at
18.degree. C. for 5 min., the maximum photographic density as determined
by an ordinary photographic density determination method is at least five
times, more preferably at least 10 times, as high as the maximum density
provided when the same amount of the silver halide emulsion is applied to
the support and exposed and the development is conducted with the
following developer B (surface type developer) at 20.degree. C. for 6
min.:
______________________________________
Internal developer A
______________________________________
Metol 2 g
anhydrous sodium sulfite
90 g
hydroquinone 8 g
sodium carbonate monohydrate
52.5 g
KBr 5 g
KI 0.5 g
water ad 1 l
______________________________________
Surface developer B
______________________________________
Metol 2.5 g
l-ascorbic acid 10 g
NaBO.sub.2 .multidot. 4H.sub.2 O
35 g
KBr 1 g
water ad 1 l
______________________________________
Examples of the internal latent-image type emulsions include
conversion-type silver halide emulsions and core/shell-type silver halide
emulsions as described in British Patent No. 1011062 and U.S. Pat. Nos.
2,592,250 and 2,456,943. Examples of the core/shell-type silver halide
emulsions include those described in Japenese Patent Public Disclosure
Nos. 47-32813, 47-32814, 52-134721, 52-156614, 53-60222, 53-66218,
53-66727, 55-127549, 57-136641, 58-70221, 59-208540, 59-216136, 60-107641,
60-247237, 61-2148 and 61-3137, Japanese Patent Publication Nos. 56-18939,
58-1412, 58-1415, 58-6935 and 58-108528, Japanese patent application No.
61-36424, U.S. Pat. Nos. 3206313, 3317322, 3761266, 3761276, 3850637,
3923513, 4035185, 4395478 and 4504570, European Pat. No. 0017148, and
Research Disclosure, No. RD 16345 (Nov., 1977).
Typical silver halides are silver chloride, silver bromide, and mixed
silver halides such as silver chlorobromide, silver chloroiodobromide and
silver iodobromide. The silver halides preferably used in the present
invention are those which are free of silver iodide. They may be those
containing less than 3 molar % of silver iodide, such as silver
chloro(iodo)bromide, silver (iodo)chloride and silver (iodo)bromide.
The average size of the silver halide grains (the diameter of the grains
when they are spherical or nearly spherical, or the edge length when they
are cubic; the average size being determined from the diameter and edge
length based on the projection areas of the grains) is preferably 0.1 to 2
.mu., particularly preferably 0.15 to 1 .mu.. The grain size distribution
range may be either narrow or wide. However, it is preferred to use
so-called "monodisperse" silver halide emulsion having such a narrow grain
size distribution that at least 90%, particularly at least 95% (in terms
of the number of the grains or the weight), of the total grains have a
diameter within the average grain diameter .+-.40% (more preferably
.+-.30%, and most preferably, .+-.20%) so as to improve the graininess and
sharpness in the present invention. To satisfy an intended gradation of
the photosensitive material, two or more monodisperse silver halide
emulsions different from each other in grain size can be used for forming
emulsion layers having substantially the same color sensitivity, or grains
having the same size but different sensitivities can be contained in the
same layer or in different layers of a multiplelayer. Further, two or more
polydisperse silver halide emulsions or a combination of a monodisperse
emulsion with a polydisperse emulsion can be used in the form of a mixture
of a multilayer.
The silver halide grains usable in the present invention may be in a
regular form such as cubic, octahedral, dodecahedral or tetradecahedral
form; an irregular crystal form such as spherical form; or a complex
thereof. Further, the grains may be tabular ones. Particulary preferred is
an emulsion in which at least 50%, based on the total projection area of
the grains, of the grains have a ratio of a length to a thickness being at
least 5, particularly at least 8. The emulsion may also comprise a mixture
of grains having various crystalline forms.
The insides or surfaces of the silver halide grains in the emulsion usable
in the present invention can be chemically sensitized by sulfur
sensitization, selenium sensitization, reduction sensitization, or noble
metal sensitization method, or by a combination of them.
The photographic emulsion to be used in the present invention is spectrally
sensitized with a photographic sensitizing dye by an ordinary method.
Particularly useful dyes are cyanin dyes, merocyanine dyes, and composite
merocyanine dyes. They can be used either singly or as a combination of
them. These dyes can be used in combination with a supersensitizer.
Examples of them and methods of using them are described in, for example,
RD 17643 (Dec., 1978) IV.
Additives can be incorporated in the present photographic emulsion for the
purposes of preventing the fogging in the course of the production,
storage or photographic processing of the photosensitive material, or
accelerating the development or stabilizing the photographic properties.
The additives include known antifoggants or stabilizers such as azoles,
mercapto compounds, thiocarbonyl compounds, azaindenes (e.g.
tetrazaindenes, preferaby 4-hydroxy-6-methyl-(1,3,3a,7) tetrazaindene),
benzenethiosulfonic acids, benzenesulfinic acids, benzenesulfonic acid
amides, purines (e.g. adenine), triazines, and phthalazinones.
More particularly, the azoles include, for example, triazoles, imidazoles,
indazoles, and thiadiazoles. The mercapto compounds include, for example,
mercaptotetrazoles, e.g. 1-phenyl-5-mercaptotetrazoles as shown below.
More detailed examples of the antifoggants, stabilizers and methods of
using them are described in, for example, U.S. Pat. Nos. 3,954,474 and
3,982,947, Japanese Patent Publication No. 52-28660, RD 17643 (Dec., 1978)
VIA to VIM and E. J. Birr "Stabilization of Photographic Silver Halide
Emulsions" (Focal Press, 1974).
##STR9##
A nucleating agent can be added to the present photosensitive material or
the processing solution therefor.
In case the nucleating agent is added to the photosensitive material, it is
preferred to add the agent to the internal latent image-type silver halide
emulsion layer. However, the nucleating agent can also be added to another
layer such as an intermediate layer, substratum layer or back layer so far
as the nucleating agent is diffused and adsorbed on the silver halide
grains in the course of the application or processing. In case the
nucleating agent is added to the processing solution, it may be
incorporated in the developer, or a pre-processing bath having a low pH
value as described in Japanese Patent Public Disclosure No. 58-178350.
As stated above, the nucleating agent to be used in the present invention
can be contained in the photosensitive material or the processing solution
for the photosensitive material. However, former is preferred to the
latter.
The present overall exposure, i.e. fog exposure, is conducted after
imagewise exposure but before the development and/or during development.
After the imagewise exposure, the photosensitive material is immersed in a
developer or preprocessing bath, and then exposed therein. Alternatively,
the photosensitive material is exposed after taking it out from the
developer or the pre-bath but before it is dried. It is most preferably to
conduct the exposure in the developer.
As a light source for the fog exposure, those having a wave length within
the sensitive range of the material can be used. Usually, any light
sources such as luminescent lamps, tungsten lamps, xenon lamps, sunlight,
etc. can be employed. When a photosensitive material sensitive to light of
the overall wave length region such as color photosensitive material is
used, a light source having a high color rendition (preferably high
whiteness) as described in Japanese Patent Public Disclosure Nos.
59-137350 and 58-70223 is preferred. The luminance of the light is 0.01 to
2,000 lux, preferably 0.05 to 30 lux, and more preferably 0.05 to 5 lux.
When the photosensitive material is composed of a high-speed emulsion, low
luminance exposure is prferred. The luminance can be controlled by
changing the luminous intensity of the light source, by reducing the
luminance with a filter, by changing the distance between the
photosensitive material and the light source, or by changing the angle
formed by the photosensitive material and the light source. The exposure
time can be reduced by using weak light in the initial stage of the
exposure and then stronger light.
It is preferable that after the photosensitive material is immersed in a
developer or pre-processing bath and then the solution has sufficiently
penetrated into the emulsion layer of the photosensitive material, the
light irradiation is conducted. The time required after the immersion and
before the fog exposure is usually 2 sec. to 2 min., preferably 5 sec. to
1 min., and more preferably 10 to 30 sec.
The exposure time for the fogging is usually 0.01 sec. to 2 min.,
preferably 0.1 sec. to 1 min., and more preferably 1 to 40 sec.
In case the nucleating agent is contained in the photosensitive material,
the amount of the agent is preferably 10.sup.-5 to 10.sup.-1 mol, and more
preferably 10.sup.-4 to 10.sup.-2 mol, per mol of the silver halide.
In case the nucleating agent is added to the processing solution, the
amount of the agent is preferably 10.sup.-8 to 10.sup.-3 mol, and more
preferably 10.sup.-7 to 10.sup.-4 mol, per liter of the solution.
The nucleating agents usable in the present invention are preferably
compounds of the following general formulae (N-I) and (N-II):
General formula (N-I):
##STR10##
wherein Z represents a non-metallic atomic group necessary for forming a
5-membered or 6-membered heterocyclic ring, Z being unsubstituted or
substituted with a substituent, R.sup.1 represents an aliphatic group,
R.sup.2 represents a hydrogen atom or an aliphatic or aromatic group,
R.sup.1 and R.sup.2 being unsubstituted or substituted with a substituent,
with the proviso that at least one of R.sup.1, R.sup.2 and Z has an
alkynyl group, acyl group, hydrazine group or hydrazone group, or R.sup.1
and R.sup.2 together form a 6-membered ring to form a dihydropyridinium
nucleas, and at least one of the substituents of R.sup.1, R.sup.2 and Z
may have X.sup.1 --L.sup.1) m, X.sup.1 being a group which accelerates the
adsorption on the silver halide grains and L.sup.1 being a divalent
connecting group, Y represents a counter ion for balancing the electric
charges, n represents 0 or 1 and m represents 0 or 1.
More particularly, the heterocyclic ring containing Z as a constituent
include, for example, quinolinium, benzothiazolium, benzimidazolium,
pyridinium, thiazolinium, thiazolium, naphthothiazolium, selenazolium,
benzoselenzolium, imidazolium, tetrazolium, indolenium, pyrrolinium,
acridinium, phenanthridinium, isoquinolinium, oxazolium, naphthoxazolium
and benzoxazolium rings.
Examples of the substituents of Z include alkyl, alkenyl, aralkyl, aryl,
alkynyl, hydroxyl, alkoxy and aryloxy groups, halogen atoms, amino,
alkylthio, arylthio, acyloxy, acylamino, sulfonyl, sulfonyloxy,
sulfonylamino, carboxyl, acyl, carbamoyl, sulfamoyl, sulfo, cyano, ureido,
urethane, carbonic ester, hydrazine, hydrazone and imino groups. A
substituent of Z is selected from, for example, the above-mentioned
substituents. When two or more substituents are selected, they may be the
same or different. Further, these substituents can further be substituted
with the above-mentioned substituents.
In addition, the substituent of Z may be a quaternary ammonium group which
forms a heterocyclic ring together with Z through a suitable connecting
group L. In such a case, the product has a dimer structure.
Among the heterocyclic rings containing Z as a constituent, preferred are
quinolinium, benzothiazolium, benzimidazolium, pyridinium, acridinium,
phenanthridinium and isoquinolinium. Particularly preferred are
quinolinium, benzothiazolium and benzimidazolium and more preferred are
quinolinium and benzothiazolium. The most preferred is quinolinium.
The aliphatic groups R.sup.1 and R.sup.2 are unsubstituted alkyl groups
having 1 to 18 carbon atoms or substituted alkyl groups having 1 to 18
carbon group in the alkyl moiety. The substituents of them are the same as
those mentioned above as the substituents of Z.
The aromatic group as R.sup.2 has 6 to 20 carbon atoms and it is, for
example, phenyl or naphthyl group. The substituents of R.sup.2 include
those mentioned above as the substituents of Z.
At least one of the groups R.sup.1, R.sup.2 and Z has an alkynyl, acyl,
hydrazine or hydrazone group, R.sup.1 and R.sup.2 are combined to form a
6-membered ring so as to form the dihydropyridinium nucleus. They may be
substituted with a substituent described above as a substituent of Z. The
hydrazine group has preferably an acyl or sulfonyl gruop as a substituent.
The hydrazone group has preferably an aliphatic or aromatic group as a
substituent.
The acyl group is preferably formly group or an aliphatic or aromatic
ketone.
Now, the alkynyl substituent of R.sup.1, R.sup.2 or Z will be further
explained in detail although it has been partially explained above. The
alkynyl substituents are preferably those having 2 to 18 carbon atoms,
such as ethynyl, propargyl, 2-butynyl, 1-methylpropargyl,
1,1-dimethylpropargyl, 3-butynyl and 4-pentynyl groups.
They may be further substituted with the above-mentioned substituents of Z,
such as 3-phenylpropargyl, 3-methoxycarbonylpropargyl and
4-methoxy-2-butynyl groups.
It is preferred that at least one of the substituents for the group
represented by R.sup.1, R.sup.2 and Z is an alkynyl or acyl group, or that
R.sup.1 and R.sup.2 are combined to form a dihydropyridinium nucleus. It
is most preferred that at least one alkynyl group is contained as a
substituent for the group represented by R.sup.1, R.sup.2 and Z.
Preferred examples of the group X.sup.1 for accelerating the adsorption on
the silver halide include thioamido group, mecapto group, and
nitrogen-containing 5- or 6-membered heterocyclic groups.
The thioamido group represented by X.sup.1 which accelerates the adsorption
is a divalent group of the formula:
##STR11##
which may be a constituent of the ring or an acyclic thioamido group. The
useful adsorption-accelerating thioamido group can be selected from those
described in, for example, U.S. Pat. Nos. 4,030,925, 4,031,127, 4,080,207,
4,245,037, 4,255,511, 4,266,013 and 4,276,364, and Research Disclosure,
Vol. 151, No. 15162 (Nov., 1976) and Vol. 176, No. 17626 (Dec., 1978).
Examples of the acyclic thioamido groups include thioureido, thiourethane
and dithiocarbamic ester groups. Examples of the cyclic thioamido groups
include groups of 4-thiazolin-2-thione, 4-imidazolin-2-thione,
2-thiohydantoin, rhodanine, thiobarbituric acid, tetrazolin-5-thione,
1,2,4-triazolin-3-thione, 1,3,4-thiadiazolin-2-thione,
1,3,4-oxadiazolin-2-thione, benzimidazolin-2-thione, benzoxazolin-2-thione
and benzothiazolin-2-thione. They can be further substituted with a
suitable substituent.
The mercapto group as X.sup.1 is either --SH group directly bonded to the
group represented by R.sup.1, R.sup.2 or Z, or --SH group bonded to a
substituent of R.sup.1, R.sup.2 or Z. The mercapto groups include
aliphatic mercapto groups, aromatic mercapto groups and heterocyclic
mercapto groups (when a carbon atom bonded to the --SH group is adjacent
to a nitrogen atom, the group is the same as a cyclic thioamido group
which is tautomeric thereto; their examples being the same as the
above-mentioned ones.
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